1. Field of the Invention
This invention is in the field of biology and more particularly in the field of cell biology.
2. Description of the Prior Art
Keratinocytes are a cell type which synthesize keratin and are able to form a stratified squamous epithelium. The most common keratinocytes are epidermal cells of the skin. Others include the cells lining the mouth, esophagus or vagina.
Although some types of mammalian cells have been serially cultivated, many mammalian types have continued to resist attempts at serial cultivation, and mammalian epidermal cells are among the latter. Although they have been grown for brief periods in primary culture, all known attempts to serially culture them have been unsuccessful. Some of the numerous literature descriptions of the cultivation of disaggregated epidermal keratinocytes in monolayers are: F. L. Vaughan and I. A. Bernstein, J. Invest. Derm., 56, 454 (1971); M. A. Karasek and M. E. Charlton, J. Invest. Derm., 56, 205 (1971); N. E. Fusenig and P. K. M. Worst, J. Invest. Derm., 63, 187 (1974); and S. H. Uspa, D. L. Morgan, R. J. Walker and R. R. Bates, J. Invest. Derm., 55, 379 (1970).
From studies of explants or short term disaggregated cell cultures, it is known that epidermal cells depend on mesenchymal cells of dermal fibroblasts for survival and growth. See J. W. Dodson, Exp. Cell Res., 31, 233 (1963); N. K. Wessells, Exp. Cell Res., 30, 36 (1963); and A. A. Moscona, In the Epidermis, Montagna et al., eds., 83 (1964). Despite such knowledge, fibroblast cells have not been successfully utilized to grow epidermal cells. In fact, because fibroblasts have invariably overrun epidermal cells in mixed cultures, investigators have usually attempted to isolate epidermal cells from fibroblasts and to grow them alone. Very little growth has taken place in such systems.
Because serial cultivation of epidermal cells has heretofore not been accomplished, it has simply not been possible to produce epidermal cells in quantity. Having to depend on skin biopsies for such cells has understandably been a severe restriction on their availability. In addition, the substitutes for epidermal cells used in such applications as covering denuded skin areas on burn victims and in the dermatological screening of drugs have not been satisfactory and suffer from many deficiencies. None of the substitutes used function entirely like natural human epidermal cells.